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That would be the problem. You have to have a ground through the pigtail to complete the coils trigger circuit. Standard Point Ignition systems use a Switched Ground , which is what the points do ..they ground the Neg side of the coil through the points and the pigtail.
There are also low cost Point conversions systems that eliminate the points while keeping the rest of the ignition system and they work very well, thus eliminating the required point replacement/adjustment maint. These keep rock solid timing and are a great improvement for short $$$$...something to consider...Pertronix makes a decent drop in unit.

Make sure to lube the rubbing block a little. The plastic part of the points assembley will wear down a lot slower and point adjustment will not go off so quickly. If not driving a real excess of miles each year the original point set up should do fine. Although I agree the aftermarket electronic trigger amp is nice. I will not go back through the thread but I hope you did change out the condensor as well. There was too much metal transfer and splattering in there by your description to ignore it. Also no one commented on your early question that I remember. I thought there was a plate that sat inside the distributor on most if not all these models. Separating the point area from the rotor area. Might be wrong though and it's been so long since I have used my earlier engined cars or even tuned one of their engines I cannot remember for sure. Anyways just glad it's running much better for you now. Enjoy the car...

She is running fine!
Thanks,
Basil

I have a 70 280 and had the same problem with the dying at stopplight problem,very dangerous. After much headscratching I found mfi was running a little too rich, one click to the lean solved problem.

Hi Arthur.

I've been following this thread and see that your knowledge might have what I'm after... My car runs well, but could be better. She is always rich and blows smoke on moderate to hard accel. and the idle has been slowly increasing so a vacuum leak might be developing. Tach has gotten jumpy which I figured out to be the points getting pitted.

I just converted from the points to Pertronix to make the pitted points and jumpy tach issue go away and while she now runs much better. However my tack is now dead because I don't know exactly how to get the tach going right. The Pertronix instructions said to use only the preresistor and stock coil (w/out internal resistance) and hook it up red to 12v and black to coil (-). SHe runs perfect, but that takes the ICU out and that leaves the tach sense wire hanging dead.....

Another thread said to tie the coil (-) to the tack sense wire (green/red stripe out of the ICU I think?) and that did get her indicating, but reading double the RPMs and is quite jumpy. So that was not the smoking gun I was hoping for.

Are you as knowledgeable in the 74 450SLs as the 280s?? I sure could use a mentor.

My timing is a mess, too. At one end of the dizzy adjustment, the timing only drops back to 14 degrees. rotating it sends it into the 30s and 40s... Plugs are very carboned up and I suspect my issues with plug may be timing related. I'm also questioning my coil... Will look for the blue spark vs an orange one tomorrow to rule out the coil. Then there is that elusive vacuum leak I am still looking for....

I have the CD, but cannot get what I'm after there either.

Ready for a challenge?

__________________
Scott
1974 450 SL (214K)

Well, after rolling the distributor back one tooth, I can now get my idle firing point to the 4 BTDC it is supposed to be at. And of course she now runs great, not as rich as before at 14 BTDC... smoking richly on hard accels.

When I changed out the faulty trigger points the other month, I must have put the dizzy back in one tooth off. Shame on me for just clamping the dist back down at the same mark on the bracket. The rotor was aligned with the mark I made, but that still didn't catch the error. And I thought that I had just developed another vacuum leak and that was why she was idling higher and running richer....

Good reminder to never just assume everything goes back the way it came out even if it appears to still be set the same....

And so I am still tach-less. Pertronix offered a different way to wire it in, but that was not successful. They said the Pert Black could go to the green ICU tach sense wire. But since that wire shows 12v, and the Pert Black needs to see ground the coil (-) side, that didn't fire at all.

So I am hoping someone has and idea of how to hook up the 5 ICU wires with the Pertronix triggering in this old 450SL so I can have my tach back.

__________________
Scott
1974 450 SL (214K)

BOSCH W5DC 0.6mm = 0.024 inch

Champion N7YCC 0.8mm = 0.031 inch

NGK BP6ES 0.7mm = 0.027 inch